Various antipollution devices adapted to be included in automotive exhaust systems are known. Two common examples are the catalytic converter and the diesel particulate filter (“DPF”). Such known antipollution devices typically include housings in which certain components are positioned. In the prior art, manufacturing the housings of these antipollution devices usually involves time-consuming (and therefore relatively costly) steps taken to address certain problems.
Catalytic converters are used for processing exhaust gases from a spark ignition engine powered by a fuel (e.g., gasoline, liquified petroleum gas, various blends of E85 and gasoline, and compressed natural gas) and from compression ignition (diesel) engines, to reduce or eliminate certain harmful gases (i.e., pollutants) in the exhaust gases. In general, the catalytic converter includes a catalyst which chemically converts certain gaseous pollutants in the exhaust to harmless compounds.
DPFs address a different pollutant. Diesel engines also produce a large volume of particulate (i.e., soot) which is also extremely detrimental to the environment. (For the purposes hereof, “exhaust” will be understood to include exhaust gases and any particulate therein.) An exhaust system including a DPF releases less soot into the environment. However, the typical DPF is very similar in construction to, and uses components similar to those used in, a catalytic converter, so that similar if not identical manufacturing methods typically are used in manufacturing the DPF and the catalytic converter.
A typical prior art antipollution device 28 is shown in FIG. 1A. (As will be described, the remainder of the drawings illustrate the present invention.) As can be seen in FIG. 1A, the prior art antipollution device 28 has a housing 26 including three portions: a main portion 38, end portions 44, 45 at each end of the housing 26, and transition portions 46, 47 connecting each end portion 44, 45 to the main portion 38 respectively. Typically, the end portions 44, 45 are sized for mating with other elements in the exhaust system, e.g., end cones “X” and “Y”, as shown in FIG. 1A. It will be understood that, in FIG. 1A, part of the housing in the main portion 38 is not shown for clarity of illustration, so that the brick 30 and the mat 32 may be shown.
It will also be understood that the prior art housing shown in FIG. 1A is exemplary only. Many different variations are well known in the art. For example, a “maniverter” (not shown) is a type of antipollution device which is mounted at or very close to a manifold on an engine, and the end portions thereof are formed accordingly. Other antipollution devices are positioned elsewhere in the exhaust system, for example, contained within a baffle subassembly (not shown) on the downstream side of the device, i.e., rather than an end cone. Accordingly, and as is also well known in the art, the housing may not necessarily be symmetric, e.g., the housing may include only one sized end portion. Similarly, because of the performance requirements and system constraints, the housing's main portion may not be symmetric with respect to its center. Also, the end portion(s) may be raised with respect to the main portion (as shown in FIG. 1A) or, alternatively, recessed relative to the main portion.
Within the main portion of the housing of a typical antipollution device is assembled a honeycomb-like structure (i.e., a “brick”) 30 most commonly made of a suitable ceramic substrate or similar material. (Other materials, e.g., stainless steel honeycombs, are also sometimes used as the substrate.) The brick 30 provides a structure to which are applied various precious metals which act as the catalyst. The brick 30 is a very fragile structure and is easily damaged, and because of this it is usually wrapped in the supportive mat 32 inside the main portion 38 of the housing 26. As is well known in the art, typically the main portion 38 of the housing 26 is sized to accommodate the preselected brick 30 and the preselected mat 32 therein.
The mat 32 is usually critical to the overall performance of the antipollution device. The mat 32 is required to seal the surfaces between the outer perimeter of the brick 30 and the inner perimeter of the housing 26 (i.e., in the main portion 38) to ensure that substantially all exhaust passes through the brick 30 and thus is exposed to the catalyst, so that the undesired emissions are processed. In addition, the mat 32 also imparts the proper forces within the housing 26 to ensure the brick 30 is not fractured due to excessive force, but is subjected to sufficient force to properly maintain and hold the brick 30 in the desired position within the housing 26 without slippage.
As is well known in the art, housings for antipollution devices are provided in a variety of shapes in cross-section. For example, in cross-section, the housings may have the following shapes: round, ovals, rectangles, squares, trapezoids, and many variations of such shapes, including irregular configurations. It is also known that antipollution device housings are often designed to receive a single brick, but alternatively housings are also often made with several bricks because of the performance requirements.
A wide variety of procedures for manufacturing antipollution devices are known in the prior art. For instance, it is known to provide a housing which is somewhat larger than required for a particular brick/mat subassembly 33. In this situation, the housing 26 is reduced in size, to the required size and shape for the individual brick/mat subassembly 33. It is also known in the prior art to provide a housing which is required to be expanded in order to accommodate the brick/mat subassembly 33.
A number of problems have arisen in connection with the known methods of manufacturing antipollution devices. The methods of the prior art have resulted in many failures due to inaccurate forming of the main portion 38, the end portion 44, 45, and the transition portions 46,47 in relation to the dimensions of the specific mat and the brick(s) which are assembled within the particular housing. For instance, if the housing is incorrectly formed too large, then the brick/mat subassembly 33 slides in relation to the housing 26, resulting in damage to the brick 30 and/or mat 32 and, as a direct consequence, the immediate failure of the antipollution device when it is used. On the other hand, if the housing 26 is sized too small or too tight, the antipollution device either cannot be assembled or the brick/mat subassembly 33 is damaged during the assembly process, which typically results in impaired performance or failure of the antipollution device.
As noted above, the end portions 44, 45 are required to be formed to be connected to other elements in the exhaust system. For a particular antipollution device housing (i.e., designed to be included in a particular exhaust system), therefore, the dimensions of the end portions 44, 45 are not subject to change—they are consistent for that housing, regardless of small variations in individual bricks and mats. However, the transition portions are, ideally, different in each housing, because the transition portions 46, 47 connect the main portion 38 (the dimensions of which are different because they are tailored to each individual brick and mat) to the end portions 44, 45 (the dimensions of which are substantially constant for a particular housing design).
It is further known that the transition portions 46, 47 of the housing 26 are also critical to ensuring optimum performance and longevity of the antipollution device. For example, if the transition portion(s) is too long (i.e., the transition portion(s) blend into the main portion), the mat 32 does not impart sufficient force evenly distributed throughout the main portion 38 to ensure retention of the internal components, i.e., the brick(s).
If a transition portion is too abrupt (i.e., too steep), depending on the circumstances, such too short transition portion may cause different problems. For example, when forming an empty housing and stuffing the brick/mat subassembly therein afterwards, if the transition portion is too steep, the mat 32 does not stay in position relative to the brick 30, and/or the edges of the mat 32 are damaged. Also, as another example, where a previously stuffed housing is reduced to GBD (described below) and the end portions are then further reduced to a smaller size, the transition portion will become too steep and natural material flow may result in the inner wall surface of the housing touching and potentially chipping (breaking) the edges of the brick, if the transition portion is not supported during forming. This happens in these circumstances because the inner diameter of the housing (i.e., in the main portion) should be supported to ensure adequate clearance between the brick and inner wall surface during the forming (reduction) of the end portions and the transition portions.
It is well known in the art that, to improve the performance of antipollution devices, each housing should be formed specifically to an individual size, shape, and form that is precisely tailored for each individual brick and mat. Also, for the reasons set out above, the transition portions of the housing need to be tailored for the individual brick and mat in order to provide antipollution devices which function properly. To accomplish this and properly size or form the housing 26, the individual and/or combined dimensions of each specific internal component are required.
Many methods are well known in the art for determining the features or dimensions of and other data related to the individual internal components or the brick/mat subassembly 33.
For example, the features of each individual brick can easily be measured from which can be derived maximum or minimum diameters or cross-sections as well as the perimeter of the brick. Diameters and perimeters are normally calculated for round bricks while cross-sections and perimeters are calculated for non-round bricks. Several known measuring processes are used to calculate these values ranging from simple mechanical measuring devices such as vernier calipers or micrometers to gauges or fixtures specifically designed to measure the brick. Typically, such devices provide data related to dimensions, weights and densities electronically, i.e., in a format readily transferred to, and useable by, other devices. Cameras and lasers and other non-contact devices are also commonly used to measure the dimensional characteristics of the brick 30 which also easily electronically report the dimensional characteristics of the part being measured. In some instances, this data has been predetermined to expedite processing of the workpiece and is provided in the form of a barcode label attached directly to or transferred with the brick 30 where it can easily be accessed.
Similarly, a number of methods for determining the relevant characteristics of each individual mat 32 are well known in the art. Common methods include using simple mechanical measuring devices such as vernier calipers or micrometers to gages or fixtures specifically designed to measure the mat 32. Other practices may use force calculating devices to determine the density of the mat material. In most instances these devices can electronically report the features or dimensional findings acquired. In some instances, this data has been predetermined and is provided in the form of a barcode label attached directly to or transferred with the mat 32 where it can easily be accessed.
Additionally it is known to preassemble the brick 30 and the mat 32 (i.e., to form a brick/mat subassembly 33) and determine the relevant overall individual brick/mat subassembly characteristics. This can be accomplished using any of the measurement methods typically used to measure the individual components as described previously. Diameters and perimeters are normally calculated for round subassemblies while cross-sections and perimeters are calculated for non-round subassemblies. The dimensional features or characteristics of the subassembly can also be calculated by recording force imparted on the subassembly at known positions to determine the optimum size required for the housing. In some instances, this data has been predetermined and provided in the form of a barcode label attached directly to or transferred with the brick/mat subassembly 33 where it can easily be accessed.
Since the performance of the assembled antipollution device depends largely on correct sizing in the main portions of the housing, where the brick/mat subassembly 33 is positioned or contained, each housing 26 is sized to a particular size (and shape) based on the components that are assembled within the housing. As noted above, however, there is no prior art method or apparatus for properly forming the main portion and the end portions, and the transition portions relative to the formed main portion.
A number of methods of inspecting the completed antipollution device or housing (i.e., with the brick 30 and mat 32 positioned in the housing 26, or prior to assembling the brick 30 and mat 32 within the housing 26), to determine acceptability of the completed device, are known. For example, one common method is to measure the completed housing and calculate the Gap Bulk Density (GBD). Another inspection method involves monitoring the amount of force that is required to push the brick/mat subassembly 33 into or out of a properly sized housing. Various other inspection methods are known. Regardless of the method, successful validation of completed assembly relies on the main portion 38 of the housing 26 having the proper size and shape relative to the size and features of the individual internal components, i.e., the specific individual brick(s) 30 and the specific individual mat 32.
Various methods of assembling the brick and the mat in the housing are known in the art. For example, one of the prior art methods is the “hard stuffed” method, in which the housing is previously formed to accommodate a selected brick 30 and a selected mat 32, and then the particular brick/mat subassembly and the particular mat for which the housing was formed are “stuffed” into the housing. This method of forming typically requires a smaller housing to be expanded to the dimensions required to accommodate the brick/mat subassembly 33.
An alternative prior art method involves stuffing the brick/mat subassembly 33 loosely into a housing that is larger than required, then to reduce the housing to the size that is required to accommodate the brick/mat subassembly 33.
If the housing is properly formed to the correct dimensions of the individual brick/mat assembly, then the assembled antipollution device satisfies the necessary GBD and/or other required inspection criteria. However, because the tolerance is relatively fine, even a small deviation from the required dimensions of the housing can result in an unacceptable assembly.
Accordingly, because the prior art method of making the antipollution device can easily result in an unacceptable assembly, significant efforts are made in the prior art to form each housing with the correct dimensions for each individual brick/mat subassembly, resulting in significant manufacturing costs. In particular, forming a housing in which the main portion, the end portions, and the transition portions are all properly formed for the individual brick(s) and mat is only possible if more than one prior art machine is used. For instance, in the prior art, the housing is often formed in a process in which at least two, and sometimes three or more different machine heads are used in an attempt to ensure that each housing is appropriately formed for a specific brick and a specific mat. Using this many machines involves a relatively high unit expense and also requires time to be spent in the manufacturing process moving the workpiece between machines. Furthermore, known methods of forming the transition portion result in the transition portion being formed based on an approximation of the dimensions of the main portion (i.e., and the dimensions of the formed chamber). Because such methods are based on approximations, however, the transition portions frequently are improperly formed, resulting in housings rejected due to failure to meet quality control standards or early failure of antipollution devices including the housings formed using such methods.